Ultrasonic transducers are sensors that convert ultrasound waves to electrical signals and electrical signals to ultrasound waves. Ultrasonic transducers that both transmit and receive are sometimes referred to as ultrasonic transceivers. Ultrasonic transducers are commonly used like radar and sonar systems to detect a target based on the response to a transmitted ultrasonic signal, for example by comparing the time interval between sending the signal and receiving an echo to determine the distance to an object or if it is in motion. Ultrasonic transducers are commonly used in cars as parking sensors to help direct the driver in reversing into a parking space.
In many cases it is of interest to keep track of living people or animals, for example to make sure that they are confined to a specific area or that they are alone in the area. Additionally it may be of interest to verify that they are alive.
In contrast in some cases it may be of interest to negate animate presence, for example to make sure that people or animals do not enter a specific area (e.g. a room) or do not come near a specific object, animal or person. Generally these objectives can be achieved by placing a guard or caretaker to watch the person, animal or object. However it would be desirable to automate this task, to reduce the need to invest in manpower.
An ultrasonic transducer could be used to detect the presence of a person, for example based on motion. However such systems do not differentiate between animate objects and inanimate objects.